Draw the first things in the vulkan testing window

[IntegratedQuantum]

This required several more changes to get working:

• support for push constants (I decided to only make the size configurable, we don't need multiple with offset for now, and as far as I can tell there is not going to be much of a performance impact from this, and from always specifying all stage flags)
• support for vertex/index buffers (this was easy after Allocate and upload data to the GPU #3510)
• Configuration of input assembly stage (fixing two TODOs from the code)
• To make it easier to introduce the new configs, I decided to finally use a struct parameter for pipeline creation which holds all the vulkan stuff
• empty star VAO is not easily convertible to vulkan (vulkan does not like empty stuff at all)
• some small fixes

Apart from the push constant config, everything else takes the exact same lines of code as the previous OpenGL config. However a most of the drawing logic (uniforms, bindings, draw command) is currently duplicated. But I don't think it's worth creating a unified API for these things, as we are going to get rid of OpenGL once the vulkan rewrite is complete.

progress towards #102